JavaScript policy

What

This policy lets you add custom JavaScript code that executes within the context of an API proxy flow. In your custom JavaScript code, you can use the objects, methods, and properties of the Apigee Edge JavaScript object model.

Where

You can attach this policy to execute custom JavaScript code at any location in the API proxy flow.

ProxyEndpoint

TargetEndpoint

PreFlow

Flow

PostFlow

PreFlow

Flow

PostFlow

Request

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Response

PostFlow

Flow

PreFlow

PostFlow

Flow

PreFlow

About

There are many use cases for the JavaScript policy. For example, you can get and set flow variables, execute custom logic and perform fault handling, extract data from requests or responses, dynamically edit the backend target URL, and much more. This policy allows you to implement custom behavior that is not covered by any other standard Edge policies. In fact, you can use a JavaScript policy to achieve many of the same behaviors implemented by other policies, like AssignMessage and ExtractVariable.

Basically, the JavaScript policy specifies the name of the JavaScript source file to execute when the step to which the policy is attached executes. The source file is always stored in a standard location within the proxy bundle: apiproxy/resources/jsc. Or, you can also store the source code in a resource file at the environment or organization level. For instructions, see Resource files. You can also upload your JavaScript through the management UI proxy editor.

JavaScript source files must always have a .js extension.

Samples

Here's a common use case: extracting data from a request body, storing it in a flow variable, and using that flow variable elsewhere in the proxy flow. Let's say you have a weather app where the user enters their zip code in an HTML form and submits it. You want the API proxy to extract the form data and dynamically add it to the URL used to call the backend service. How would you do this in a JavsScript policy?

Note: If you want to try out this example, we assume you've created a new proxy in the proxy editor. When you create it, just give it a backend service URL of: http://www.example.com. For this example, we're going to rewrite the backend URL dynamically. If you don't know how to create a new proxy, refer to the getting started tutorial. .

In the dialog, select JavaScript and give the script a name, like js-example.

Paste the following code in the code editor and save the proxy. The important thing to notice is the context object. This object is available to the JavaScript code anywhere in the proxy flow. It's used to obtain flow-specific constants, to call useful get/set methods, and for more operations. This object part is of Edge's JavaScript Object Model. Note, too, that the target.url flow variable is a built-in, read/write variable that is accessible in the Target Request flow. When we set that variable with the "weather" API URL, Edge makes its backend call to that URL. We've essentially rewritten the original target URL, which was whatever you specified when you created the proxy (e.g., http://www.example.com).

From the New Policy menu, select JavaScript.

Give the policy a name, like target-rewrite. Accept the defaults, and save the policy.

If you select the Proxy Endpoint Preflow in the Navigator, you'll see that the policy was added to that flow.

In the Navigator, select the Target Endpoint PreFlow icon.

From the Navigator, drag the JavaScript policy onto the Request side of the Target Endpoint in the flow editor.

Save.

Call the API like this, substituting your correct org name and proxy name as appropriate:

One final thing, let's take a look at the XML definition for the JavaScript policy used in this example. The important thing to note is that the <ResourceURL> element is used to speicfy the JavaScript source file to execute. This same pattern is used for any JavaScript source file: jsc://filename.js. If you're JavaScript code requires includes, you can use one or more <IncludeURL> elements to do that, as described later in this reference.

You can add a <Property> element in configuration, then retrieve the element's value with JavaScript at runtime.

Use the element's name attribute to specify the name with which to access the property from JavaScript code. The <Property> element's value (the value between the opening and closing tags) is the literal value that will be received by the JavaScript.

In JavaScript, you retrieve the policy property value by accessing it as a property of the Properties object, as in the following:

Configure the property. Here, the property value is the variable name response.status.code.

<Javascript> Attributes

Specifies the maximum time (in milliseconds) that the script is permitted to execute.

Note: For free trial accounts, execution time is limited to 200 ms.

N/A

Required

The following attributes are common to all policy parent elements.

Attribute

Description

Default

Presence

name

The internal name of the policy. Characters you can use in the name are restricted to: A-Z0-9._\-$ %. However, the Edge management UI enforces additional restrictions, such as automatically removing characters that are not alphanumeric.

Optionally, use the <DisplayName> element to label the policy in the management UI proxy editor with a different, natural-language name.

N/A

Required

continueOnError

Set to false to return an error when a policy fails. This is expected behavior for most policies.

Set to true to have flow execution continue even after a policy fails.

false

Optional

enabled

Set to true to enforce the policy.

Set to false to "turn off" the policy. The policy will not be enforced even if it remains attached to a flow.

true

Optional

async

Note: This attribute does not make the policy execute asynchronously.

When set to true, policy execution is offloaded to a different thread, leaving the main thread free to handle additional requests. When the offline processing is complete, the main thread comes back and finishes handling the message flow. In some cases, setting async to true improves API proxy performance. However, overusing async can hurt performance with too much thread switching.

<DisplayName> element

Use in addition to the name attribute to label the policy in the management UI proxy editor with a different, natural-language name.

<DisplayName>Policy Display Name</DisplayName>

Default:

N/A

If you omit this element, the the value of the policy's name attribute is used.

Presence:

Optional

Type:

String

<IncludeURL> element

Specifies a JavaScript library file to be loaded as dependency to the main JavaScript file specified with the <ResourceURL> element. The scripts will be evaluated in the order in which they are listed in the policy. Your code can use the objects, methods, and properties of the JavaScript object model.

Include more than one JavaScript dependency resource with additional <IncludeURL> elements.

If your JavaScript files are stored at the organization or environment level, be sure they were uploaded correctly with cURL using the -F option or as a file attachment through a REST client. Content-Type is multipart/form-data. For more information, see Resource files.

Attributes

Example

<ResourceURL> element

Specifies the main JavaScript file that will execute in the API flow. You can store this file at the API proxy scope (under /apiproxy/resources/jsc in the API proxy bundle or in the Scripts section of the API proxy editor's Navigator pane), or at the organization or environment scopes for reuse across multiple API proxies, as described in Resource files. Your code can use the objects, methods, and properties of the JavaScript object model.

<ResourceURL>jsc://my-javascript.js</ResourceURL>

Default:

None

Presence:

Required

Type:

String

Example

Flow Variables

This policy does not populate any variables by default; however, you can set (and get) flow variables in your JavaScript code by calling methods on the context object. A typical pattern looks like this: